1. Field of the Invention
The present invention relates to a television receiver and more particularly, to a picture stabilizing circuit for a semiwide-screen television receiver which can compensate for bending of vertical lines at the right and left corners of a display screen due to a partially extended horizontal amplitude caused by a high-voltage variation corresponding to a picture brightness variation.
2. Description of the Related Art
A semiwide-screen television receiver has an enlarged horizontal picture size with a 12.8.times.9 aspect ratio (AR), i.e. the ratio of width to height, in comparison to that of the existing 4.times.3 AR standard television receiver. The semiwide-screen television receiver can display horizontal information pertaining to a 12.times.9 AR television broadcasting signal at its maximum AR by minimizing the overscanning rate in the horizontal direction. To achieve this, a technique for stabilizing the edge portions of the picture is required since the overscanning rate of the television receiver in the horizontal direction should be reduced from approximately 9.3% for the standard television receiver, to approximately 3.2% for the semiwide-screen television receiver.
FIG. 1 is a schematic circuit diagram of a conventional television receiver. Referring to FIG. 1, a video processing section 10 receives a luminance (Y) signal and a chrominance (C) signal, and outputs the luminance signal and red (R), green (G), and blue (B) color signals to a cathode ray tube (CRT) driving section 12 which drives a CRT 14 to display a picture on the CRT 14. The video processing section 10 outputs a horizontal sync signal HD to a horizontal driving section 16 which drives a horizontal output section 18 to control the horizontal scanning on the screen through a horizontal deflection coil DC. A horizontal deflecting force is compensated for by an east/west (E/W) compensation signal which is obtained by amplifying an E/W signal provided from video processing section 10.
Meanwhile, a high-voltage circuit section 22 supplies a high voltage HV induced in a secondary winding of a flyback transformer FB to an anode of CRT 14 through a diode D.
According to the conventional television receiver as constructed above, if a relatively wide range of the picture is bright, the horizontal amplitude thereof becomes extended, causing the vertical lines of the picture to be bent as shown in FIG. 2. This is because the straight force of an electron beam becomes weakened in the bright region of the picture. If the straight force is weakened, the deflecting force is correspondingly strengthened, causing the trace of the electron beam to be angled outside by a degree .theta. as shown in FIG. 3. As a result, the deflecting force should be lowered corresponding to the high voltage variation in order to secure picture linearity in the bright region.
The video processing section 10 receives from the high-voltage circuit section 22 an auto brightness limit (ABL) signal which is obtained by detecting the voltage signal of the secondary winding of the flyback transformer FB. The video processing section 10 compensates for the picture size in accordance with the ABL signal. However, such an ABL type compensation circuit has difficulty in providing a rapid response due to its time delay characteristic. Also, while compensation for one horizontal period can be achieved, it is difficult to achieve compensation for one vertical period.
As mentioned, it is to be appreciated that in a standard television receiver having a horizontal overscanning rate of 9.3%, a distorted picture, due to an unstable high voltage caused by the variation of the picture brightness is typically not displayed on the edge portions of the screen. However, in a semiwide-screen television receiver having a horizontal overscanning rate of 3.2%, the right and left edge portions of the picture may be distorted due to the high-voltage variation caused by the picture-brightness variation, thereby deteriorating picture quality.